Insulation Between Rafters Flat Roof

The insulation is below the deck but above the plasterboard.

Insulation between rafters flat roof.

Then install r 30 fiberglass batts between the rafters. Install ventilation baffles into the space between the rafters before you install the insulation usually by stapling into place. Breathing roof with low resistance lr underlay with this option insulation fully fills the rafter space without an airspace between the insulation and type lr underlay. If your attic is going to be converted into livable space then you will need to insulate the roof rafters.

The flexible nature of gmw means that the roll or batts can be accurately cut and friction fitted between the rafters thereby minimising air gaps and maximising thermal performance. A cold deck flat roof will typically require insulation to be installed between the roof joists to comply with building regulation requirements. Unless the joists are exceptionally deep there is also likely to be a requirement to install insulation to the underside of the joists as the upper 50mm of joist space is usually required to be left clear for ventilation purposes. If 180mm is to be installed then 100mm board might be introduced between the rafters there has to be a minimum 25mm air gap between the insulation and the underside of the tiles or slates with an 80mm board running across the rafters.

Isover glass mineral wool gmw is another option for the between rafter insulation as a roll or batt. Refurbishing an existing timber joisted flat roof which has no insulation. Installing stacks of rigid foam between rafters is slow fussy work but it might make sense for a do it yourselfer. With a warm roof the usual process is to split the insulation into two layers.

Insulation between the rafters can be designed in two ways. Framing this out and buying 30 r fiberglass insulation will cost you about 50 more than just buying 5 inches of polyiso equivalent of 30 r. Rigid foam also does a better job of stopping air flow as long as it s carefully sealed at the edges. This limits the maximum thickness of the insulation between the rafters to between 50mm and 175mm.

A cold flat roof is one where the insulation is between or between and below the roof joists. The flexible nature of gmw means that the roll or batts can be accurately cut and friction fitted between the rafters thereby minimising air gaps and maximising thermal performance. Isover glass mineral wool gmw is another option for the between rafter insulation as a roll or batt. Most types of rigid foam insulation have a higher r value per inch than fiberglass batts.

Piling up pieces of rigid foam. This generally would not be a sufficient thickness to achieve the u values required to meet building regulations and more insulation would need to be added. Common rafter depths range from 100mm to 200mm.